A conventional optical pulse waveform shaper such as shown in the Laser Handbook, page 365, published by the Laser Gakkai (Laser Society) in 1982 is illustrated in FIG. 1. It includes three beam splitters 1, 2, 3 for splitting an input beam L, and a pair of reflectors 4, 5 and three beam splitters 6, 7, 8 for combining the split beams L.sub.1, L.sub.3, L.sub.5, L.sub.6 to provide an output beam L.sub.9.
The operation will now be described below.
An input optical pulse beam L is split into a reflected beam L.sub.1 and a transmitted beam L.sub.2 by the beam splitter 1. The transmitted beam L.sub.2 is split into a reflected beam L.sub.3 and a transmitted beam L.sub.4 by the beam splitter 2. The transmitted beam L.sub.4 is split into a reflected beam L.sub.5 and a transmitted beam L.sub.6 by the beam splitter 3. Thus, the respective beams L.sub.1, L.sub.3, L.sub.5, L.sub.6 are different from each other in phase and attenuation. The beam L.sub.1 is reflected by the reflector 5 and combined with the beam L.sub.3 into a beam L.sub.7 by the beam splitter 6. The beams L.sub.7 and L.sub.5 are combined into a beam L.sub.8 by the beam splitter 7. The beam L.sub.8 is combined with the beam L.sub.6 reflected by the reflector 4 into an output beam L.sub.9 by the beam splitter 8. Thus, the output beam L.sub.9 has been shaped to have a desired intensity distribution.
In such conventional optical pulse waveform shaper, part of the beam L.sub.3 reflected by the beam splitter 2 is transmitted by the beam splitter 6 resulting in an optical pulse energy loss. Part of the beam L1 reflected by the reflector 5 is reflected by the beam splitter 6 resulting in an optical pulse energy loss. In addition, two sets of beam splitters 1-3 and 6-8 for splitting and combining, respectively, must be designed and manufactured. Moreover, it is not easy to align all these optical axes.
Although the optical pulse waveform L.sub.9 of a desired intensity distribution may be shaped when the input optical pulse waveform L has an even intensity distribution, it has been impossible to provide an optical pulse waveform of a desired intensity distribution for an input optical pulse waveform of an intensity distribution in which the central portion leads the peripheral portion or vice versa.
Accordingly, it is an object of the invention to provide an optical pulse waveform shaper capable of combining the split optical pulse beams with little loss.
It is another object of the invention to provide an optical pulse waveform shaper capable of providing an optical pulse waveform of a desired intensity distribution from that of a given intensity distribution with little loss.